会的来挑战下~
问题描述：
会的来挑战下~
When an object is thrown vertically upwards,its height "h" varies with the time "t" according to the equation h=20t - 5t^2.At what times will the heighy be 10m?Use the formula to solve the quadratic equation.
Formula就是x=[-b±√(b^2-4ac)]/(2a)
答
当h=10m,
20t - 5t^2=10
即 - 5t^2+20t-10=0
运用公式,即
x=[-b±√(b^2-4ac)]/(2a)
得 x=2-√2
或 x=2+√2